Apparatus for separating the rare gases krypton and xenon from the atmosphere



- w. DENNIS 1,945,366 APPARATUS FOR SEPARATING -THE RARE GASES KRYPTON AND XENON FROM THE ATMOSPHERE Original Filed May 5, 1932 Jan. 30, 1934.

. 26 f7 2 All? 4 49 OXYG'EN ATTORNEY5 Patented Jan. 30, 1934 UNITED STATES APPARATUS FOR SEPARATING THE RARE GASES KRYPTON AND XENON FROM THE ATMOSPHERE Wolcott Dennis, Stamford, Conn., assignor to Air Reduction Company, Incorporated, New N. Y., a corporation of New York York,

Original application May 5, 1932, Serial No.

Divided and this application March 23, 1933. Serial No. 662,187

2 Claims.

recovery. of krypton and xenon from the atmos phere. This application is a division of my copending application Ser. No. 609,425 filed May In the well-known methods for recovering oxygen and nitrogen from air by liquefaction and rectification, the air, after compression and cooling, is liquefied, and the vapors risingfrom the liquid are rectified by contact with further portions of the liquid with the object of producing vapor consisting substantially of nitrogen and a liquid containing the oxygen constituent. Owing to the fact that the boiling points of the rare gases krypton and xenon are higher than that of oxygen, these elements accumulate in the oxygen liquid at the bottom of the rectification column. In ordinary practice this liquid is evaporated and the krypton and xenon pass ofi with the oxygen. The amount of krypton and xenon in the atmosphere is so small that these elements appear merely as impurities in commercial oxygen.

It is the object of the present invention to provide a simple and eifective apparatus for recovering a liquid concentrate relatively rich in krypton and xenon from the liquid oxygen which accumulates at the bottom of an ordinary rectification column. The concentrate may be vaporized and subjected to further purification for the purpose of providing krypton and xenon for commercial purposes.

In carrying out the invention, any system of liquefaction and rectification may be utilized to secure the initial separation of the air into nitrogen and liquid oxygen containing krypton and xenon. Several systems are well-known and are in commercial use. The recovery of the concentrate relatively rich in krypton and xenon is accomplished by subjecting the oxygen liquid containing krypton and xenon from the bottom of the primary rectification column to an auxiliary rectification with vapors therefrom. Owing to the difference in boiling points of oxygen and of krypton and xenon, the oxygen separates as a vapor and the liquid is enriched in krypton and xenon. This liquid concentrate, rich in krypton and xenon, is subjected to a further partial vaporization and is finally withdrawn at the end of the auxiliary rectification cycle. During this final vaporization the supply of oxygen liquid containing krypton and xenon is cut off. The cycle is then repeated by again introducing the supply of oxygen liquid containing krypton and xenon to the auxiliary rectification column. Durthe auxiliary rectification, a small amount of This invention relates to the separation and liquid enriched in krypton and xenon remains on the trays of the auxiliary rectification column, and this liquid is washed downwardly by the fresh portion. of the oxygen liquid and is thus accumulated with the liquid residue which is withdrawn from the bottom of the auxiliary rectification column at the conclusion of the auxiliary rectification cycle.

Any suitable apparatus may be employed for the purpose of the invention, and it is to be particularly understood that the invention is not limited to any method of effecting the initial separation of nitrogen and oxygen from the atmosphere. For the purpose of clarity, the invention is illustrated in the accompanying drawing as embodying the well-known Claude apparatus for separating oxygen and nitrogen from.

The invention will be better Q understood by reference to the following descripthe atmosphere.

' through the partitions '7 and 8 and surrounds the lower ends of the tubes 12.

Air in the liquid and gaseous phases is supplied through a pipe 15 in the manner hereinafter described to the compartment 9. The gaseous air passes upwardly through the tubesll in indirect contact with liquid which accumulates about the tubes, and by backward return condensation a partial separation is effected, resulting in a liquid enriched in oxygen'which flows downwardly into the compartment 9. This liquid,

together with the liquid introduced through the pipe 15, is carried upwardly by a pipe 16 under control of a valve 17 and is delivered onto the trays 6 at an intermediate point in the rectification column. It fiows downwardly over the trays in contact with vapors rising from the accumulated liquid in the bottom of the column above the partition 7.

The uncondensed residue from the tubes 11 passes into the head 13 and thence downwardly,

through the tubes 12 and is condensed therein to a liquid consisting of nitrogen which flows, into the well 14 and thence through a pipe 18 and valve 19 into the top of the column 5. This liquid nitrogen flows downwardly over the trays 6 and washes from the rising vapors the oxygen constituent thereof, which is condensed and joins the downwardly flowing liquid which finally accumulates in' the bottom of the column above the partition 7. Vapors consisting principally of nitrogen escape as an eifiuent through a pipe 20 at the top of the column. The liquid, rich in oxygen and containing the krypton and xenon initially present in the air, overflows through a pipe 21 into the compartment 10 between the partitions '1 and 8. In the normal operation of a liquefaction column, this liquid in the compartment 10 is evaporated by heat exchange with the air passing through the tubes 11 and escapes through a pipe 22 as the oxygen product of the operation.

It will be understood that the air undergoing liquefaction and rectification in the primary column 5 is first compressed and cooled in the usual compressors and interchangers (not shown). In the compressed and cooled state it is delivered through a pipe 23 to an exchanger 24 and circulates about the tubes 25 and 26 therein, where it is cooled by heat exchange with products leaving the system. The compressed and cooled air is delivered through a pipe 27 and a portion thereof passes through an expansion engine 28 where if is expanded to a lower pressure and thereby cooled. It is delivered from the expansion engine 28 through a pipe 29 to the pipe 15 and thus enters the compartmentQ at the bottom of the primary column 5. Another portion of the compressed and cooled air passes through a pipe 30 into a liquefier 31 and-about the tubes 32 and 33 therein, through which cold products of the separation are conveyed. The air at the initial pressure is thus cooled and liquefied, and the' liquid escapes through a pipe 34 and valve 35 and is delivered through the pipe 15- to the compartment 9 at the bottom of the primary column 5.

- The nitrogen from the primary column is delivered by the pipe 20 to a compartment 36 at one end of the liquefier 31, passes through the tubes 32 to a compartment 37 at the opposite end of the liquefier, thence through a pipe 38 to a compartment 39 at one end of the exchanger 24' and through the tubes 25 to a compartment 40 at the opposite end of the exchanger. The nitrogen having thus given up its cold to the incoming air is delivered through a pipe 41 and valve 42 to a storage receptacle or to the atmosphere as may be desired.

The oxygen product from the pipe 22 is delivered by a pipe 43 to a compartment 44 at one end of the liquefier 31 and thence through the tubes 33 to a compartment 45 at the. other end of the liquefier. It passes through a pipe 46 to a com-- partment 47 at one end of the exchanger 24, and thence through the tubes 26 to a'compartment 48 at the opposite end of the exchanger. Having been thus warmed by heat exchange with the in- .coming air, the oxygen product is delivered the usual form and with a partition 53 forming a lower compartment 54. A pipe 55 delivers liquid from the upper rectifying section of the auxiliary column 51 to the compartment 54. Liquid oxygencontaining krypton and xenon is delivered through a pipe 56 controlled by a valve 57 from the compartment 10 of the primary column 5 to a receptacle 58 at the top of the auxiliary column 51. The receptacle 58 has an outlet 59 at its bottom, through which the liquid flows onto the trays 52. A liquid level gauge 60 is connected to the receptacle 58 to indicate the level of the liquid therein.

In the compartment 54 at the bottom of the auxiliary column 51 a coil 61 is provided and is connected by a pipe 62 controlled by a valve 63 to the pipe 34, so that liquid from the liquefier 31 at'a temperature somewhat higher than the liquid in the compartment 54 can be diverted through the coil 61 to evaporate that liquid. The other end of the coil is connected by a pipe 64 controlled by a valve 65 to the pipe 15, the liquid and any vapors formed being thus returned to the compartment 9 of the primary column 5. At the lower end of the auxiliary column 51 a reduced extension 66 is provided in which the liquid residue, rich in krypton and xenon, is accumulated and from which it is withdrawn through a pipe 67 controlled by a valve 68. The liquid can be evaporated and treated for further purification in any suitable apparatus (not shown). A liquid level gauge 69 is connected to the bottom of the extension 66 and tothe compartment 54,

so that the operator may observe the level of the the invention, the primary column 5 produces continuously liquid oxygen containing krypton and xenon which accumulates in the compart-,

ment 10 at the bottom of the column. This liquid is withdrawn through the pipe 56 and valve 57 and is delivered to the top of the auxiliary column 51. The liquid is permitted to flow into the auxiliary column for a limited period, for example an hour, more or less. The flow of liquid through the pipe 56 is then stopped. Meanwhile, some vaporization occurs in the compartment 10 and the vapor is withdrawn through the pipe 22. Owing to the difierence in boiling points of oxygen and of krypton and xenon, only a small part of the krypton and xenon escapes through the pipe 22 and thence through the pipe 43 to the oxygen storage receptacle.

In the auxiliary rectification cycle, air, all or part liquid, is admitted through the pipe 62, to the coil 61, and because of the diiference in temperatures between the liquid in the coil and the liquid surrounding the coil, the latter is partially vaporized and the vapors rise through the usual openings provided therefor in the partition 53' and trays 52 in contact with the liquid flowing downwardly on the trays. As the result of the rectification, the rising vapors'are freed from krypton and xenon and finally escape from the top of the auxiliary column into the pipe 43 by which they are withdrawn as the oxygen product of the operation. The descending liquid is enriched in krypton and xenon. When the flow of liquid is stopped by closing the valve 57, the remaining liquid enriched in krypton and xenon continues to evaporate and is gradually reduced in volume until it fills substantially only the extension 66 at the bottom of the auxiliary column, except for such portions of the liquid as may remain on the trays 52. At this point the liquid residue which is rich in krypton and xenon is withdrawn from theextension 66 through the pipe 67 and valve 68 as the krypton and xenon concentrate.

The cycle is then repeated by opening the valve 57 and permitting a further portion of the liquid oxygen containing krypton and xenon to flow into the auxiliary column 51. This flow of liquid washes any liquid which may remain on the trays 52 into the compartment 54 of the auxiliary column 51. When the rectification in the auxiliary column has proceeded to the extent hereinbefore indicated, the valve 57 is again closed, and the liquid is evaporated to produce a residue rich in krypton and xenon which is again withdrawn.

By the operation as described, the recovery of krypton and xenon from the atmosphere is accomplished in a simple, economical and satisfactory manner. The operation involving the intermittent delivery of the oxygen liquid containing krypton and xenon and final evaporation of the liquid residue is more effective than a continuous vaporization and rectification of the liquid accumulating in the bottom of the primary column 5. The reduced extension at the bottom of the auxiliary column is an important improvement, since it facilitates the collection of the small quantity of residual liquid rich in krypton and xenon. It is possible to recover by the procedure described 70% or more of the krypton and xenon originally present in the air treated.

Various changes may be made in the arrange-- ment of the apparatus and in the procedure as described, without departing from the invention or sacrificing any of the advantages thereof.

I claim:

1. In an apparatus for recovering krypton and xenon from the atmsophere, a primary rectification column having a compartment for the accumulation of oxygen liquid containing krypton and xenon, an auxiliary rectification column, a pipe having a valve therein connecting the compartment with the auxiliary rectification column, means for supplying heat to the liquid in the auxiliary rectification column, an outlet for the vapors from the auxiliary rectification column, a reduced extension at the bottom of the auxiliary rectification column in which liquid enriched in krypton and xenon can accumulate, and a pipe having a valve therein for withdrawing the liquid.

2. In an apparatus for recovering krypton and xenon from the atmosphere, a primary rectification column having a compartment for the accumulation of oxygen liquid containing krypton and xenon, an auxiliary rectification column, a pipe having a valve therein connecting the compartment with the auxiliary rectification column, means for supplying heat to the liquid in the auxiliary rectification column, an outlet for the vapors from the auxiliary rectification column, a reduced extension at thebottom of the auxiliary rectification column below the level of evaporation therein, in which liquid enriched in krypton and xenon can accumulate, and a pipe having a valve therein for withdrawing the liquid.

WOLCOTT DENNIS. 

